The IEEE standard 802.11a pertains to wireless local area networks (WLAN), and adopts Orthogonal Frequency Division Multiplexing (OFDM). OFDM is a technology that transmits data as multiple signals simultaneously over a single transmission path. OFDM spreads the data over a large number of carriers that are spaced apart at precise frequencies. Typically, a transmitter transforms frequency based data into the time-domain using an Inverse Fast Fourier Transform (IFFT) algorithm prior to transmission. A receiver then transforms a received packet back to the frequency domain using a Fast Fourier Transform (FFT) algorithm. The total number of sub-carriers translates into the number of points of the IFFT/FFT. In a wireless networking environment, OFDM has inherent advantages over a signal carrier system in a frequency-selective fading channel, such as high spectral efficiency, resiliency to RF interference, and lower multi-path distortion.
Under 802.11a, packets are mapped into a framing format suitable for sending and receiving user data and management information between two or more stations. This format includes a preamble field that is comprised of a preamble of short symbols (short preamble) and a preamble of long symbols (long preamble). Subsequent to the preambles is a signal field, followed by multiple data fields. At a receiver, incoming packets are sampled, and the samples are entered into a delay chain or delay line for processing to locate the field boundaries.
A standard 802.11a timing recovery algorithm uses a long delay chain, typically comprised of a plurality of pipelined registers, to store a large number of data samples. In general, a register pipeline can be useful for applications in digital signal processing and wireless telecommunications systems. With respect to timing acquisition of a 802.11a packet, samples are often tapped from registers in the delay chain for use in computations.